It is known that hexamethylene diamine (HMD) can be made by a process in which butadiene is hydrocyanated in the presence of a nickel catalyst to yield a reaction product that contains adiponitrile (ADN), and the ADN is hydrogenated using an iron-containing catalyst to yield a reaction product that contains HMD.
It is also known that the hydrocyanation step can be carried out in the presence of certain phosphorous-containing promoter compounds, such as tritolyl phosphite (TTP) and the more recently described monodentate and bidentate compounds. U.S. Pat. Nos. 3,496,215; 3,496,217; 3,496,218; 5,512,695; 5,512,696; 5,523,453; 5,663,369; 5,693,843; 5,723,641; and 5,821,378 describe some of these monodentate and bidentate compounds.
The hydrocyanation step can lead to the production of certain impurities, such as 2-cyanocyclopentylideneimine, which are difficult to separate from the ADN by distillation. One way to address this problem is to treat the ADN-containing hydrocyanation reaction product with ozone to convert the impurities to more easily separable compounds. The ozone treated hydrocyanation reaction product can then be purified by standard industrial methods such as dehydration and distillation. See Canadian Patent 672,712.
Published International Patent Applications WO 00/03972 and 00/12460 describe methods for producing HMD in which ADN is hydrogenated to yield a reaction product that contains unreacted ADN, HMD and aminocapronitrile (ACN). The HMD and ACN are separated from the reaction product, and unreacted ADN is returned to the hydrogenation reactor. The unreacted ADN can be treated, if desired, with ozone, among others.
Published German patent application DE 19636765 A1 (1998) describes processes for removing phosphorus-containing compounds from ADN made by the hydrocyantion of butadiene. These processes are said to be useful for decreasing the deactivation of iron-based catalysts which are used to hydrogenate the ADN. These processes involve distillation of the ADN, extraction of the ADN, treatment of the ADN with base, and treatment of the ADN using adsortpion or chemisorption.
Iron is a known catalyst for, among other things, the synthesis of ammonia, which is a process that is said to be closely related to hydrogenation. Phosphorous is a known catalyst poison, although it may be possible to detoxify phosphorous by chemically bonding it to other elements to produce a so-called shielded structure in which there are no unshared electron pairs. See Maxted, E. B., The Poisoning of Metallic Catalysts, Advances in Catalysis, Vol. III, p 129, Academic Press, 1951.
It is known that ozone can attack nucleophilic phosphorous. In particular, it is known that ozone can react with triphenylphosphine to produce the corresponding oxide in good yield. See Bailey, P. S., Ozonation in Organic Chemistry, Vol. II, p 201, Academic Press, 1982.
The use of phosphorous-containing ligands in hydrocyanation of butadiene can result in the presence of these ligands and their degradation products in the resulting ADN-containing reaction product. If this reaction product is subsequently hydrogenated in the presence of an iron-containing catalyst, the phosphorous may result in a diminution of the useful life of the iron-containing catalyst. There is a need in the art for a process for treating such an ADN-containing reaction product to reduce its ability to diminish the life of the iron-containing catalyst used in the subsequent hydrogenation step.